Role of the Bacillus subtilis W23 stress response extracytoplasmic function sigma factor σM in two essential processes - teichoic acid biosynthesis and cell division

Détails

Demande d'une copie
ID Serval
serval:BIB_43343
Type
Thèse: thèse de doctorat.
Collection
Publications
Titre
Role of the Bacillus subtilis W23 stress response extracytoplasmic function sigma factor σM in two essential processes - teichoic acid biosynthesis and cell division
Auteur(s)
Minnig K.
Directeur(s)
Mauël C.
Codirecteur(s)
Lazarevic V.
Editeur
[s.n.]
Institution
Université de Lausanne, Faculté de biologie et médecine
Adresse
Lausanne
Statut éditorial
Acceptée
Date de publication
2004
Langue
anglais
Nombre de pages
143
Notes
REROID:R003695316; 30 cm ill.; Old school value: Université de Lausanne
Résumé
ABSTRACT
This work allowed to characterize the regulation of the tarA gene, participating in the biosynthesis of the major teichoic acid (TA), as well as several aspects concerning the role and regulation of the extracytoplasmic function (ECF) sigma factor σM in Bacillus subitlis W23.
In B. subtilis, cell wall contains two essential polymers, peptidoglycan and TA. B. subtilis strains 168 and W23 are endowed with a chemically different major TA, I. e. poly(glycerol-phosphate) or poly(ribitol-phosphate), respectively. The tar (teichoic acid ribitol) genes specifying the biosynthesis of the major TA in B. subtilis W23 are organized as two divergently transcribed operons tarDF and tarABIJKL, the latter being controlled by two promoters designated P tarA-ext. Analysis of promoter activities and gene expression during batch culture in rich medium and under phosphate limitation allowed to identify several factors involved in tarA regulation: (i) The P tarA-int promoter directs two expression increases at the beginning and the end of the transition between exponential and stationary growth phase. These were shown to be caused by the successive action of two ECF σ factors, σX and σM. (ii) The PtarA-ext promoter is repressed under phosphate starvation by the PhoPR two-component system, whereas the P tarA-int promoter is upregulated by the action of σM under the same conditions. (iii) tarA expression is increased in a conditioned medium suggesting the participation of cell density signals in tar gene regulation.
Investigation of the role and regulation of σM showed its importance in batch culture growth as well as in cell wall stress response. Besides their role in TA biosynthesis, σM and σX are involved in cell division, controlling among others expression of an essential division initiation protein, DivIC. Concomitant inactivation of σX and σM leads to delays in chromosome segregation and septation as well as to an impairment of septal cell wall, as revealed by electron microscopy. Furthermore, like other division related genes, sigM expression was demonstrated to be inversely proportional to growth rate.
In the absence of the appropriate stimulus, ECF σ factors are generally sequestered by a transmembrane anti-σ factor. Once the stimulus detected, the σ factor is released and modulates the transcription of the genes belonging to its regulon. As suggested by the effects of their overexpression, the products of the two genes downstream of sigM, yhdL and yhdK, seem to work together to negatively regulate σM.
σM activity in strains 168 and W23 is fundamentally different, possibly due to differences in cell wall composition. In contrast to strain 168, σM is activated in strain W23 in phosphate-depleted conditions, a phenomenon indirectly dependent on PhoPR, the two-component system responsible for the adaptation to phosphate starvation. Moreover, in strain 168, σM activity remains low in rich medium, but in W23 it is sharply induced upon entry into stationary phase.
In accordance with the current knowledge we propose that σM responds to global changes in cell wall structure as a result of diverse stresses or batch culture growth phase transitions. A model of σM activation and function in B. subtilis W23 is discussed.
In the absence of the appropriate stimulus, ECF σ factors are generally sequestered by a transmembrane anti-σ factor. Once the stimulus detected, the σ factor is released and modulates the transcription of the genes belonging to its regulon. As suggested by the effects of their overexpression, the products of the two genes downstream of sigM, yhdL and yhdK, seem to work together to negatively regulate σM.
σM activity in strains 168 and W23 is fundamentally different, possibly due to differences in cell wall composition. In contrast to strain 168, σM is activated in strain W23 in phosphate-depleted conditions, a phenomenon indirectly dependent on PhoPR, the two-component system responsible for the adaptation to phosphate starvation. Moreover, in strain 168, σM activity remains low in rich medium, but in W23 it is sharply induced upon entry into stationary phase.
In accordance with the current knowledge we propose that σM responds to global changes in cell wall structure as a result of diverse stresses or batch culture gr